This invention relates generally to suction dewatering systems for paper making machines wherein the felt is passed over suction slots defined by laterally spaced wear strips. The invention is concerned in particular with an improved arrangement for adjusting the widths of the suction slots by laterally shifting the relative positions of the wear strips.
The known arrangements for laterally shifting the wear strips all suffer from various drawbacks. For example, in the arrangement disclosed in U.S. Pat. No. 3,836,428 (McConaughy) some of the wear strips are provided with centrally located longitudinally extending dovetail slots whereas other wear strips are provided with dovetail slots which are laterally offset. These slots are adapted to slide over upstanding fixed mounting ribs located along the sides of the suction openings. Different suction slot widths can be obtained by arranging the wear strips in different combinations and by turning the wear strips with laterally offset slots end for end. One problem with this arrangement, however, is that a number of different types of wear strips must be kept in inventory. Moreover, the turning of wear strips end for end is awkward and time consuming. Also, there are only a limited number of suction slot widths available with this type of arrangement.
In an attempt at avoiding these problems, arrangements of the type disclosed in U.S. Pat. Nos. 4,278,497 (Mellen) and 4,280,869 (Eckerdt) have been developed.
In both of these arrangements, the wear strips have cam slots which extend obliquely in relation to the suction slot. In the '497 arrangement, the wear strips are movable longitudinally and the oblique cam slots coact with oblique stationary guide rails, whereas in the '869 arrangement the wear strips are longitudinally stationary and the obligue cam slots receive longitudinally movable cam members. In either case, however, the oblique cam slots produce a lateral shifting of the wear strips and a corresponding adjustment in the width of the suction slots. The difficulty with these arrangements, however, is that if the wear strips on opposite sides of a given suction slot are to be adjustable, then they must be machined differently, i.e., with right or left hand oblique cam slots. This again increases inventory costs. Moreover, the oblique cam slots make it difficult if not impossible to longitudinally remove and replace the wear strips without disturbing other components. Thus machine maintenance is made much more difficult, often resulting in protracted and costly down time.